Does a DPF light fail an MOT?

The lamp on its own is not a listed defect, but what causes it usually is. Since 2018 a diesel fitted with a particulate filter fails if the exhaust emits visible smoke of any colour, and it fails outright if the tester finds evidence the filter has been removed or hollowed out. A car with a blocked filter will also often fail the smoke opacity limits.

How do I clear a DPF light myself?

Drive for around 20 minutes at a steady 40mph or above, keeping the revs above about 2,000 in a lower gear than you would normally use. That raises exhaust temperature enough for the filter to burn off its soot. If the lamp does not clear after two attempts, or the car loses power, it needs a garage.

Is it illegal to remove a DPF?

Removing it makes the car fail its MOT, and using a vehicle on the road with the filter removed is an offence because it no longer meets the emissions standard it was type-approved to. Testers are specifically instructed to look for cut and rewelded filter casings.

Can a blocked DPF be cleaned rather than replaced?

Often, yes, and it is worth asking before agreeing to a replacement. A garage can attempt a forced regeneration, which drives the burn-off cycle on a diagnostic tool rather than waiting for the right sort of journey, and specialists can chemically clean a filter off the car. What decides it is whether the filter is loaded with soot or with ash: soot burns off and ash does not, so a filter that has been slowly ashing up over a long life eventually needs replacing whatever you do to it.

Dashboard warning light

Diesel particulate filter light

Last updated 27 July 2026

Quick answer

The diesel particulate filter has collected more soot than it can hold and needs to burn it off. Caught early this is fixed by a longer, faster drive; ignored, it turns into a blocked filter costing four figures.

What to do: Get it checked within days
Can you drive?: Only to a garage

Why it is amber

A system has reported a malfunction, or something needs attention. The car is usually still driveable, but the fault will not clear itself and several amber lamps are an automatic MOT failure.

What turns it on

The filter traps soot and periodically burns it off by raising exhaust temperature, which needs sustained speed. Short journeys never get hot enough, so soot accumulates until the pressure difference across the filter crosses a threshold and the lamp asks the driver for a longer run.

What to do about it

Drive for 20 minutes at a steady 40mph or more where it is legal and safe to do so, ideally in a lower gear than usual to keep the revs above 2,000. Most cars clear the lamp this way.
Do not switch the engine off mid-regeneration if you can avoid it, as an interrupted burn leaves the filter part-loaded and the lamp comes straight back.
If the lamp stays on after a good run, or turns red, or the engine goes into reduced power, stop using the car for short trips and get it to a garage.
Check the oil. Interrupted regenerations dump diesel into the sump, and an overfull, fuel-diluted oil level is its own engine-destroying problem.

Can you keep driving?

Only to a garage

An amber DPF lamp is effectively an instruction to drive, not to stop, and a decent motorway run is the fix. What you must not do is carry on with the same short trips that caused it, because the next stage is a blocked filter and a forced regeneration or replacement.

What causes it

A pattern of short, cold journeys that never allow a regeneration to complete
Regenerations repeatedly interrupted by switching off part way through
A failing differential pressure sensor misreading how full the filter is
A faulty EGR valve or turbo actuator producing more soot than normal
The wrong oil specification, which ashes the filter prematurely

Does it fail an MOT?

Not on its own — but what causes it often does.

The lamp itself is not a listed defect. What fails cars is what causes it: a diesel fitted with a particulate filter fails on visible smoke of any colour, fails if the smoke opacity limits are exceeded, and fails outright if the tester finds the filter has been cut open or removed.

Fault codes that turn this light on

The lamp tells you which system reported a problem. The code stored behind it names the check that failed, which is the difference between knowing something is wrong and knowing where to look. These are the ones that commonly sit behind this symbol.

P2002 Diesel particulate filter not trapping soot properly
P2452 Electrical fault in the particulate filter pressure sensor circuit
P244ADiesel Particulate Filter Differential Pressure Too Low
P242F Particulate filter blocked with ash that will not burn off

Got a different code? Look it up — the index covers every standard OBD-II code.

Common questions

Does a DPF light fail an MOT?: The lamp on its own is not a listed defect, but what causes it usually is. Since 2018 a diesel fitted with a particulate filter fails if the exhaust emits visible smoke of any colour, and it fails outright if the tester finds evidence the filter has been removed or hollowed out. A car with a blocked filter will also often fail the smoke opacity limits.
How do I clear a DPF light myself?: Drive for around 20 minutes at a steady 40mph or above, keeping the revs above about 2,000 in a lower gear than you would normally use. That raises exhaust temperature enough for the filter to burn off its soot. If the lamp does not clear after two attempts, or the car loses power, it needs a garage.
Is it illegal to remove a DPF?: Removing it makes the car fail its MOT, and using a vehicle on the road with the filter removed is an offence because it no longer meets the emissions standard it was type-approved to. Testers are specifically instructed to look for cut and rewelded filter casings.
Can a blocked DPF be cleaned rather than replaced?: Often, yes, and it is worth asking before agreeing to a replacement. A garage can attempt a forced regeneration, which drives the burn-off cycle on a diagnostic tool rather than waiting for the right sort of journey, and specialists can chemically clean a filter off the car. What decides it is whether the filter is loaded with soot or with ash: soot burns off and ash does not, so a filter that has been slowly ashing up over a long life eventually needs replacing whatever you do to it.

This is general guidance, not a diagnosis. Manufacturers draw the same system differently and reuse symbols for more than one function, so check the handbook for your own car before acting on anything here.

Check what your car has actually failed on

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